The casting method using a lost foam is a method in which a casting pattern obtained by applying a mold wash to the surface of a foam pattern is embedded in foundry sand, and a molten metal is then poured into the casting pattern, thereby losing the foam pattern and replacing the foam pattern with the molten metal, thereby making a casting. It may be considered that this casting method using a lost foam is most suitable for forming a hole (referred to as a “cast hole”) in the casting by performing casting.
In the casting method using a lost foam, during casting, large thermal loads from the surroundings act on the mold wash applied to the surface of the hole of the foam pattern (a portion where the hole is formed by casting) and on the foundry sand packed in the hole. In addition, various external forces (e.g., a molten metal hydrostatic pressure, a dynamic pressure by molten metal flow, etc.) act thereon from the molten metal.
In the case where the mold wash itself does not withstand the above-described thermal loads or external forces, a casting defect called “seizure” in which the mold wash is damaged and the molten metal seeps into the foundry sand packed in the hole and fuses with the foundry sand may occur. In particular, when it is contemplated to form a small hole with a diameter of 12 mm or less by casting, the frequency of generation of seizure due to the damage of the mold wash becomes high, so that it becomes difficult to form a small hole with a good finish.
Then, Patent Literature 1 discloses a mold wash composition for lost foam in which a chromaticity of the L*a*b* colorimetric system and a measured value by a Brookfield viscometer are set to the appropriate ranges. According to this, a coating film with a uniform thickness is obtained, and therefore, metal penetration generated in the case where the coating film is thin is avoided.
In addition, Patent Literature 2 discloses a mold wash composition for lost foam in which a composition is set to an appropriate range. According to this, metal penetration defects and transfer of a drooped line can be prevented from occurring.
In addition, Patent Literature 3 discloses a mold wash composition for lost foam containing an ore whose endothermic peak temperature (° C.) by differential thermal analysis falls within a specified range. According to this, the generation of residue defects and metal penetration defects can be prevented from occurring.